In the transportation, of so called dangerous goods, such as liquid chemicals, paints and toxic liquids, it is imperative that measures be adopted to reasonably guarantee the sealed integrity of the liquid carrying containers and more especially the sealing covers or lids for such containers which are typically cylindrical, as in the case of paint cans, for example. Such measures must include protection against the presence of abnormal hydrostatic pressures within a container as may occur from impact, extreme pressure differentials or indentation of the container's walls or by liquid vaporization in order that the sealed integrity thereof be maintained and leakage of liquid contents be avoided.
Recently the United Nations Committee on the transportation of dangerous goods adopted certain regulations which provide a common and uniform measuring system for specifying packaging and container requirements to be applied internationally. In general such requirements differ from existing U.S. governmental regulations in that are directed to the performance of the package rather than to the type of materials involved therein. Among such United Nations regulations are new performance tests having to do with internal pressures of the containers, which in the present case concern generally cylindrical metal paint cans having removable friction locked lids or covers. In brief, this test requires a container with lid or cover in place to be filled with water and subjected to predetermined internal pressures for a specific duration. No leakage may occur during the time period in order for the container to pass the test. Based on the vapor pressure of the product being packaged, the internal testing pressure is broken down into three groupings, which in the case of a multi-friction fit paint container or its equivalent, requires the sealed container to withstand an internal pressure of 14.5 psi (100 KPa) for a period of five minutes.
Since such a multi-friction fit container is not engineered to be a pressure vessel, without some modification it will not normally comply with the United Nations test regulations.